The present invention relates to a sputtering target, and more particularly to improvements in a composite sputtering target wherein a plurality of target pieces of different kinds of materials are arrayed.
Heretofore, sputtering technology has been extensively known as a technique for forming thin films on specified base materials. In the sputtering technology, various attempts have been made to form, not only a thin film which is constituted by a single component-substance, but also a thin film composed of multiple constituents such as an alloy or the like. In such sputtering technology, in the case where a target which is constituted with different components in a composition ratio deviating from stoichiometric amounts and is difficult to prepare, for example, a target of molybdenum and silicon, or in the case where an alloy target body of predetermined composition ratio is difficult to prepare because of a great difference in the melting points or vapor pressures of the alloy components, a composite sputtering target in which a plurality of kinds of constituents are respectively arranged in divided fashion is used (refer to, for example, Japanese Patent Laid-Open Publication No. 46631/1987).
As the composite target mentioned above, there has been known a target wherein a plurality of kinds of wedge-like target pieces are alternately combined into the shape of a disk, or a target body wherein elongated target pieces are alternately arrayed into the shape of a rectangular plate.
The deposition of a film employing the composite sputtering target as stated above has the advantage that the composition ratio of the film to be formed can be changed at will by changing the kinds and combination of the target pieces. In the case of, for example, a disk-shaped target body, the composition ratio is held identical in the radial direction of the target, so that the composition of the deposited film becomes uniform, and a deposited film conforming to the composition ratio of the target is obtained.
On the other hand, however, when the erosion of a target by sputtering does not proceed uniformly as in the case of the rectangular target body, a discrepancy inevitably arises between the composition ratio of the deposited film and that of the target, and sometimes a non-uniform region is present. This will be further explained below.
The above phenomenon will be elucidated in the case of employing a prior art composite target as shown in FIG. 1. The composite target 30 of the prior art includes Ta pieces 31 and Mo pieces 32 alternately arrayed in a predetermined composition ratio. When the target is used for sputtering, usually the area enclosed by the two-dot chain lines indicated in FIG. 2 forms an erosion region 33. In this case, in the middle part of the target in the longitudinal direction thereof, the composition ratio of the target corresponds exactly to that of the produced film. At both the end parts of the target in the longitudinal direction thereof, however, the lines of the sputtering depict curves or circular arcs, with the result that the erosion region 33 forms a shape affording non-uniform distribution of film constituents. This incurs the disadvantage that the fail to correspond exactly. In the case of the example shown in FIG. 2, the Ta content of the target is higher than in the desired composition at both the end parts thereof. In consequence, the produced alloy film exhibits non-uniform physical properties at both its end parts in the longitudinal direction thereof, thereby posing the problems that the efficiency of film formation and the available percentage of finished product are lower.